Influence of the hemicellulose fraction on thermal and photochemical discoloration of paper
| Main Authors: | , |
|---|---|
| Format: | Article |
| Language: | English Slovak |
| ISBN: | ISBN 0-88748-374-7 |
| Online Access: | http://www.viks.sk/chk/CTCS_577_586.doc |
| Abstract: | Summaries. Hemicellulose is a major contributor to the thermally induced darkening of bleached pulp.1 Rollinson2 found the rate of formation of colored, acidic, water-soluble material to parallel discoloration of the pulp and also observed that the water-soluble components accounted for 50-60% of the discoloration that occurred during accelerated thermal aging; about 23% of these components were demonstrated to be oligosaeeharides composed of simple sugars typical of hemicellulose. The effect of hemicelluloses has also been studied with model compounds;3,4 all aldoses and glucuronic acid were found to contribute to thermally induced discoloration. In contrast, relatively little attention has been given to the influence of hemicelluloses upon photochemically induced discoloration. As part of our general studies on the effect of light on paper, the present investigation was designed to compare the discoloration induced-thermally and photochemically-as a result of the presence of hemicellulose materials. Test sheets were prepared principally from Whatman No, 42 filter paper saturated with hemicellulosic fractions that had been isolated from various unaged or thermally aged pulps by LiOH extraction.5 Another set of test sheets was prepared by saturation of filter paper with commercially prepared arabinogalactan and especially isolated acetylxylan. (The term "added-on" will be used to refer to the occlusion of the various fractions to the filter paper as a result of saturation.) Finally, a series of handsheets was made from the pulps of different -cellulose contents (10.5-1.5%) that were obtained by the extraction of bleached sulfate pulp with different strengths of caustic solution. The various test papers thus prepared with different concentrations of hemicellulosic components were evaluated for their tendency to discolor upon exposure to visible and near-UV radiation (daylight and black-light fluorescent lamps) and to heat. Conclusions. Tests using hemicellulosic extracts from several different pulp stocks indicate that little if any discoloration is caused by exposure of these components to visible and near-UV radiation or even radiation at 254 nm (UV). In the continuing quest to understand the causes of discoloration in paper, these results support the contention that the tendency of hemicelluloses to lead to discoloration is primarily a thermally induced effect. |
|---|---|
| ISBN: | ISBN 0-88748-374-7 |
